Overhead electric transmission systems

ABSTRACT

A flexible stranded body, such as an electric conductor of an overhead electric transmission or distribution system, comprises at least one stranded layer of elongate elements of metal or metal alloy, at least one elongate compartment within and extending throughout the length of the stranded body and, loosely housed in the elongate compartment, at least one separate optical fibre and/or at least one optical bundle. Preferably, the elongate compartment extends within a circumferentially rigid central core which is surrounded by the stranded layer or layers but it may be a bore in an elongate element of a stranded layer or an elongate space bounded by two adjacent elongate elements.

This application is a continuation of my copending application Ser. No.904,557, filed May 10, 1978 now abandoned.

This invention relates to bare overhead flexible electric transmissionconductor of the kind which comprise one or more than one stranded layerof elongate elements of electrically conductive metal or metal alloy andwhich are adapted to be freely supported from spaced supports in longlengths.

It is an object of the present invention to provide a bare overheadflexible electric transmission conductor which includes at least oneoptical guide for the transmission of the ultra-violet, visible andinfra-red regions of the electromagnetic spectrum, which regions, forconvenience, will hereinafter all be included in the generic term"light"; it is an especial, but not exclusive, object of the inventionto provide a flexible stranded body which includes at least one opticalwaveguide for use in the communications field adapted for transmissionof light having a wavelength within the range 0.8 to 1.3 micrometers.

According to the invention a flexible stranded body comprises at leastone stranded layer of elongate elements of metal or metal alloy, atleast one elongate compartment within and extending throughout thelength of the stranded body and, loosely housed in the elongatecompartment or at least one of the elongate compartments, at least oneseparate flexible optical guide.

The or each flexible optical guide may be a separate optical fibre or anoptical bundle.

The or each optical fibre may be of glass or other transparent materialwhose refractive index is arranged to decrease over at least a part ofthe radius of the fibre in a direction towards the outer surface of thefibre or it may be of composite form comprising a core of transparentmaterial clad throughout its length with another transparent material oflower refractive index which, but total internal reflection of lightbeing transmitted along the fibre, confines at least a major proportionof the light within the core. A composite optical fibre is generally,but not necessarily, made of two glasses of different refractiveindices, the glass forming the core having a higher refractive indexthan the glass forming the cladding; the refractive index of the glassof the core may gradually decrease towards the outer surface of the coreover at least a part of the distance between the central axis of thecore and its outer surface. In an alternative form of composite fibrethe core may be a transparent liquid having a higher refractive indexthan that of the cladding. All such optical fibres generally, but notnecessarily, have diameters lying in the range 100 to 150 μm. The oreach optical fibre is usually of substantially circular cross-sectionbut, in some circumstances, it may be of non-circular cross-section.

By the expression "optical bundle" is meant a group of optical fibres ora group of fibres including at least one optical fibre and at least onenon-optical reinforcing fibre or other reinforcing elongate member. Eachoptical fibre of the optical bundle may be used independently as aseparate light guide, each with its own modulated light source anddetector, or a plurality of optical fibres of a bundle may be usedtogether as a single light guide, with a single light source.

By virtue of being housed loosely in the elongate compartment, limitedrelative movement between the or each separate optical fibre and thestranded body and/or between the or each optical bundle and the strandedbody can take place when the stranded body vibrates, oscillates or isotherwise flexed as may, for example, occur in the case when an overheadelectric conductor or other freely supported flexible stranded body issubjected to winds. Limited relative movement between the or eachseparate optical fibre and the stranded body and/or between the or eachoptical bundle and the stranded body can also occur when the strandedbody is subjected to a charging tensile load during and after itsinstallation due to forces imposed on it by winches and brakes, etc.,which are used in tensioning the stranded body to obtain a predeterminedsagging condition; after installation, changes in tensile load in thestranded body can also occur due to changes in external loading and intemperature. Limited relative movement between the or each separateoptical fibre and the stranded body and/or between the or each opticalbundle and the stranded body can also occur whilst the stranded body isin service and creep gives rise to non-elastic extension of the strandedbody.

In one preferred aspect of the invention, an elongate compartment iswithin and extends throughout the length of a substantiallycircumferentially rigid central core and the or each layer of bareelongate elements of metal or metal alloy surrounds the central core. Inone preferred embodiment of this aspect of the invention, the centralcore comprises two or more bare elongate members of metal or metal alloyassembled together to form an elongate body having a central bore whichconstitutes the elongate compartment and, to prevent or limit the extentof lateral movement between the elongate members, each may be of such atransverse cross-sectional shape that they inter-engage. The centralcore may be built up of two bare elongate members, each having atransverse cross-sectional shape approximating to a semi-annulus, theabutting faces of the two members being so shaped that theyinter-engage; in this case, preferably, for ease of manufacture, the twomembers are of identical transverse cross-sectional shape. In onealternative embodiment of the aforesaid aspect of the invention, thecentral core is a flexible tube comprising a stranded layer of bareelongate elements of metal or metal alloy, each element having atransverse cross-section approximating to a sector of an annulus. Inthis case, to prevent or limit the extent of lateral movement betweenthe elongate members, the flexible tube so formed is immediatelysurrounded by a second stranded layer of bare elongate metal elements,each of which may be of a similar transverse cross-section to that ofthe elongate elements of the flexible tube, the direction of lay of thissecond layer being of opposite hand to that of the stranded layerconstituting the flexible tube.

In another alternative embodiment of the aforesaid aspect of theinvention, the substantially circumferentially rigid central corecomprises a flexible tube formed by at least one helically woundflexible elongate member of metallic and/or non-metallic reinforcingmaterial, for instance a wire or metallic tape and/or compacted glassfibres impregnated with resin.

In a third alternative embodiment of the aforesaid aspect of theinvention, the central core is a single bare elongate member ofsubstantially U-shaped transverse cross-section, the space between thelimbs and base of the U constituting the elongate compartment. To retainthe or each optical fibre and/or optical bundle in the elongatecompartment, one or each of the limbs of the U may be folded inwardly(for instance, by passing the member through an appropriate die or diesprior to application of the stranded layer or layers of elongateelements) so that the gap between the free ends of the limbs is at leastpartially closed; alternatively, the or each optically fibre and/oroptical bundle is retained in the elongate compartment by means of atleast one tape of metal or metal alloy which is helically applied to, orlongitudinally applied to and transversely folded around, the U-shapedelongate member.

In a second aspect of the invention, the or each elongate compartmentextending throughout the length of the flexible stranded body is a boreformed in an elongate element of the stranded layer or of at least oneof the stranded layers or an elongate space bounded by at least twoadjacent elongate elements of the stranded layer or layers. In apreferred embodiment of this second aspect of the invention, theflexible stranded body comprises at least two stranded layers ofelongate elements of metal or metal alloy, the directions of lay ofadjacent layers being of the same or opposite hand, and the bore orbores and/or elongate space or spaces is or are in, or between adjacent,elongate elements of an inner or the innermost stranded layer. The oreach elongate element having a bore in which at least one separateoptical fibre and/or at least one optical bundle is loosely housed maybe of suitable transverse cross-section but, where the optical fibre orfibres and/or the optical bundle or bundles is or are loosely housed inan elongate space bounded by two adjacent elongate elements, theseelongate elements preferably have a transverse cross-sectional shapeapproximating to a sector of an annulus. For ease of manufacture,preferably one of the abutting faces of two adjacent elongate elementshas an elongate recess which is closed by the flat surface of the otherof the abutting faces to form an elongate space.

In all cases, usually outer layers or the outermost layer of two or morestranded layers of elongate elements each comprise a stranded layer ofwires, each of substantially circular cross-section, but in somecircumstances the wires of at least the outermost layer may each have atransverse cross-sectional shape approximating to a sector of anannulus.

Although the or each separate optical fibre and/or optical bundle mayitself be loosely housed in the or an elongate compartment, preferablythe separate optical fibre or fibres and/or bundle or bundles is or aresupported by a flexible elongate carrier member which is loosely housedin the elongate compartment so that the required relative limitedmovement between the separate optical fibre or optical fibres and/orbundle or bundles and the flexible stranded body can take place.

Preferably, the flexible elongate carrier member comprises an extrudedelongate body of rubber or plastics material which has, extendingthroughout its length, at least one bore in which at least one separateoptical fibre and/or at least one optical bundle is or are looselyhoused and, preferably also, this extruded elongate body has at leastone elongate reinforcing member embedded in and extending throughout thelength of the body. In one form of flexible carrier member, the axes ofthe bore or bores and of the reinforcing member or members may lie in asubstantially common plane. In another form of flexible carrier member,a plurality of bores may be arranged around a central elongatereinforcing member. The or each reinforcing member may be a wire or astranded group of wires or it may be of non-metallic material. Where theor a bore loosely houses two or more separate optical fibres and/oroptical bundles, they may be secured on or within at least onesubstantially flat flexible support member which is itself looselyhoused in the bore.

One alternative flexible elongate carrier member that may be usedcomprises a plurality of separately forward tubes or rubber or plasticsmaterial assembled together and surrounded by an outerprotective sheath,at least one of the tubes loosely housing at least one separate opticalfibre and/or at least one optical bundle. At least one elongatereinforcing member may be assembled with the plurality of tubes.

Another alternative flexible elongate carrier member that may be usedcomprises at least one substantially flat flexible support member on orwithin which two or more separate optical fibres and/or optical bundlesare secured. The substantially flat flexible support member ispreferably in the form of at least one tape, for instance of paper orplastics material, glass or of metal or metal alloy. In somecircumstances, it is preferred that the or each tape is of a materialhaving a coefficient of thermal expansion approximating to that of thematerial or materials of the optical fibres. For example, where theoptical fibres are of a silica-based material, the or each tape may beof steel.

Where the flexible support member consists of a single tape, theseparate optical fibres and/or optical bundles may be secured byadhesive to one surface of the tape; viewed in transverse cross-sectionthe tape may be corrugated so that it has a plurality of troughsextending along its length, in each of some or all of which a separateoptical fibre or optical bundle may be secured. Where the flexiblesupport member consists of two tapes, one overlying the other, theseparate optical fibre and/or optical bundles may be sandwiched betweenthe two tapes and may be secured by adhesive to at least one of theadjacent surfaces of the tapes; one or each of these two tapes may betransversely corrugated as described above. Where one or each of twotapes is transversely corrugated, the two tapes may be so bondedtogether that the optical bundles and/or separate optical fibres aresecured within the flexible support member so formed but are capable oflimited movement within the troughs in which they lie. Where opticalfibres and/or bundles are secured within a substantially flat flexiblesupport member, preferably the flexible support member comprises asingle tape of plastics material with the separate optical fibres and/oroptical bundles wholly or partially embedded in it.

As a means of initially identifying any optical bundle and/or separateoptical cable secured side-by-side on or within at least onesubstantially flat flexible support member, the support member may carrya longitudinally extending datum mark on its surface and/or at least oneof the optical bundles and/or optical fibres may be assymmetricallypositioned with respect to the or each other optical bundle and/oroptical fibre so that it constitutes a longitudinally extending datum.

The or each separate optical fibre and/or optical bundle, and whenpresent the flexible elongate carrier member thereof, may be of a lengthsubstantially greater than that of the elongate compartment in which itis loosely housed but preferably the or each separate optical fibreand/or optical bundle, the carrier member thereof when present, and theelongate compartment are of equal or approximately equal lengths.

Where the flexible stranded body is an overhead electric conductor,preferably the stranded elongate elements are of copper or a copperalloy, or aluminium or an aluminium alloy but, in some circumstances,the elongate elements of at least one layer of stranded elements may beof high tensile steel or other metal or metal alloy of high tensilestrength or at least some of the elongate elements of said layer orlayers may be of one metal or metal alloy of high tensile strength andthe remainder of said elongate elements may be of another metal or metalalloy, or other metals or metal alloys, of high tensile strength.

To provide for relative sliding movement between adjacent elongateelements of the stranded layer or layers and to assist in preventingwater from gaining access to the interior of the flexible stranded bodyand thereby reduce risk of corrosion of the elongate elements, theinterstices between the elongate elements may be filled with a greasymaterial.

The flexible stranded body of the present invention is especiallysuitable for use as an earth conductor of an overhead electrictransmission line and, because it may be manufactured to have the sameor approximately the same properties of sag and tension as those ofconventional overhead conductors of substantially the same overalldiameter, it provides the important advantage that the flexible strandedbody can be used to replace an earth conductor or other overheadelectric conductor of an existing overhead electric transmission systemthereby to provide a communication means in the system. Thus, theinvention provides a relatively inexpensive communication link betweenstations, substations and other locations along an electric transmissionsystem.

Accordingly, the invention also includes an overhead electrictransmission or distribution system which includes at least one overheadstranded conductor incorporating an optical guide as hereinbeforedescribed.

Where the overhead stranded conductor incorporating an optical guide isan earth conductor of the system, the earth conductor may be suspendedbetween the tops of towers or other supporting structures or it may besupported between the towers or other supporting structures at positionsbelow the cross-arms of the towers.

The invention will be further illustrated by a description, by way ofexample, of eight forms of overhead stranded electric conductor withreference to the accompanying drawings, in which:

FIGS. 1 to 8, respectively, are transverse cross-sectional views of theeight forms of overhead conductor;

FIG. 9 is a transverse cross-sectional view of an optical fibre elementused in the overhead conductors shown in FIGS. 7 and 8, drawn on agreatly enlarged scale, and

FIGS. 10 to 15, respectively, are transverse cross-sectional views ofsix alternative forms of optical fibre element for use in an overheadconductor.

Referring to the drawings, the overhead stranded conductor shown in FIG.1 comprises a central core 1 built up of two elongate members 2 ofaluminium-based alloy each having a transverse cross-sectional shapeapproximating to a semi-annulus and together defining a bore 6. Eachmember 2 has extending along one of its limbs a substantially V-shapedgroove 3 and along the other of its limbs a rib 4 of complementaryshape, the arrangement being such that the rib of one member engages inthe groove of the other member so that lateral movement between themembers is substantially prevented. The central core is surrounded bytwo stranded layers 5 of round wires of aluminium-based alloy, thedirections of lay of the stranded layers being of opposite hand. Looselyhoused in the bore 6 is a plastics tube 7 having a bore 8 in which isloosely housed an optical fibre 9 of a length substantially equal tothat of the bores 6 and 8.

In the overhead stranded conductor shown in FIG. 2, a central core 11 isconstituted by a single elongate aluminium alloy member 12 ofsubstantially U-shaped cross-section, the space 16 between the limbs ofthe U constituting an elongate compartment. Surrounding the central core11 are three stranded layers 15 of round wires of aluminium-based alloy,the directions of lay of adjacent stranded layers being of oppositehand. A plastics tube 17 having a bore 18 is loosely housed in theelongate compartment 16 and an optical fibre 19 is loosely housed in thebore 18.

The overhead stranded conductors shown in FIGS. 3 and 4 are similar inconstruction to the overhead conductor shown in FIG. 2 except for theform of the central core and, for convenience, components of theoverhead conductors shown in FIGS. 3 and 4, respectively, that aresimilar to those of the overhead conductor shown in FIG. 2 have beengiven references greater by 10 and by 20 than the references of thecorresponding components of the overhead conductor shown in FIG. 2. Inthe overhead conductor shown in FIG. 3, the central core 21 is a tube 22formed by transversely folding a strip of aluminium-based alloy. In theoverhead conductor shown in FIG. 4, the central core 31 is constitutedby a single elongate aluminium alloy member 32 of substantially U-shapedcross-section, the gap between the free ends of the limbs of the U beingpartially closed to retain the plastics tube 37 in the elongatecompartment 36.

The overhead stranded conductor shown in FIG. 5 has a central core 41comprising a inner stranded layer 42 of elongate elements ofaluminium-based alloy, each element having a transverse cross-section ofa shape approximating to that of a sector of an annulus and thedirections of lay of the layers being of opposite hand. Surrounding thestranded layers 42 and 43 are two stranded layers 45 of round wires ofaluminium-based alloy, the directions of lay of these two strandedlayers being of opposite hand. Loosely housed in the bore 46 is anoptical fibre element 44 comprising an extruded plastics body 47 havinga bore 48 in which are loosely housed three optical fibres 49. Two steelreinforcing wires 50 are embedded in the body 47 on opposite sides ofthe bore 48, the axes of the bore and of the reinforcing wires lying ina common plane.

In the overhead stranded conductor shown in FIG. 6, the central core 51comprises a flexible tube formed by a closely helically wound steel wire52. The central core 51 is surrounded by three stranded layers 55 ofround wires of aluminium-based alloy, the directions of lay of adjacentlayers being of opposite hand. Loosely housed in the bore 56 of thecentral core 51 is an optical fibre element 54 comprising an extrudedplastic body 57 having a bore 58 and embedded reinforcing wires 60, theaxes of the bore and wires lying in a common plane, and, loosely housedin the bore, two optical fibres 59.

The overhead stranded conductor shown in FIG. 7 comprises a core 61 ofseven steel wires, a stranded layer 62 of aluminium elements 63, each ofa transverse cross-section approximating to a sector of a circle, sosurrounding the core that it is loosely housed within the bore formed bythe stranded layer and, surrounding are layer 62, a stranded layer 65 ofround wires of aluminium-based alloy, the directions of lay of thelayers 62 and 65 being of opposite hand. Each element 63 has a bore 64in which is loosely housed an optical fibre element 66 of the form shownin FIG. 9. The optical fibre element 66 comprises an extruded plasticsbody 67 of a transverse cross-section of elongate shape having a bore 68and embedded reinforcing wires 70, the axes of the bore and reinforcingwires lying in a common plane, and, loosely housed in the bore 68, twooptical fibres 69.

The overhead stranded conductor shown in FIG. 8 is of similarconstruction to that shown in FIG. 7 and where appropriate, similarcomponents have been given references greater by ten. In the overheadconductor shown in FIG. 8, each bore 74, loosely housing an opticalfibre element 66 of the form shown in FIG. 9, comprises a recess in oneof the abutting faces of two adjacent elements 73, of aluminium-basedalloy, the recess being closed by the other of said abutting faces.

In each of the overhead stranded conductors shown in FIGS. 1 to 8,instead of the separate fibre or fibres loosely housed in the bore of aplastics tube or instead of the plastics tube loosely housing opticalfibres or other optical fibre elements, any of the optical fibreelements shown in FIGS. 10 to 15 may be employed, the optical fibreelements being drawn on a greatly enlarged scale to clarify theirstructure. The optical fibre element shown in FIG. 10 comprises aflexible tape 82 of plastics material which has secured by adhesive toone of its major surfaces four optical fibres 81 which are spaced apartand extend substantially parallel to the axis of the tape. In theoptical fibre element shown in FIG. 11, four optical fibres 91 aresandwiched between and secured by adhesive to the adjacent surfaces oftwo flexible tapes 92, 93 of plastics material. The tape 93 has alongitudinally extending rib 97 to provide for ready identification ofany optical fibre 91. The optical fibre element shown in FIG. 12comprises a flexible plastics tape 102 which, viewed in transversecross-section, is so corrugated that it has a plurality of troughs 104extending along its length in each of which an optical fibre 101 issecured by adhesive. The optical fiber element shown in FIG. 13comprises a corrugated flexible plastics tape 112 which has a pluralityof troughs 114 extending along its length, the troughs being closed by aflat plastics tape 113 which is bonded to the peaks 115. Optical fibres111 are secured by adhesive in the troughs 114. In the optical fibreelement shown in FIG. 14, optical fibres 121 are sandwiched between, andsecured by adhesive in the troughs 124, 128 of, two flexible corrugatedplastics tapes 122, 123 whose peaks 125, 129 are secured together byadhesive. To provide for reday identification of any optical fibre 121,the tape 123 has a longitudinally extending rib 127. The array shown inFIG. 15 comprises a plastics tape 132 in which four optical fibres 131extending side-by-side are wholly embedded. The tape 132 has alongitudinally extending rib 137 to provide for ready identification ofany optical fibre 131.

What we claim as our invention is:
 1. An overhead flexible electrictransmission conductor (as claimed in claim 3, wherein) adapted to befreely supported from spaced supports in long lengths, comprising asubstantially circumferentially rigid central core comprising at leasttwo bare elongate members of metal or metal alloy assembled together toform an elongate body having a central bore extending throughout thelength of the core and constituting an elongate compartment, each bareelongate member of the central core (is) being of such a transversecross-sectional shape that they inter-engage at least to limit theextent of lateral movement between the elongate members; at least oneseparate flexible optical guide loosely housed in the elongatecompartment; and, surrounding the central core, at least one strandedlayer of helically wound bare elongate elements of metal or metal alloy.2. An overhead flexible electric transmission conductor as claimed inclaim 1, wherein the central core comprises two inter-engaging bareelongate members, each having a transverse cross sectional shapeapproximating to a semi-annulus.
 3. An overhead flexible electrictransmission conductor as claimed in claim 2, wherein the two bareelongate members of the central core are of identical transverse crosssectional shape.
 4. An overhead flexible electric transmission conductor(as claimed in claim 2, wherein the central core is) adapted to befreely supported from spaced supports in long lengths, comprising asubstantially circumferentially rigid central core consisting of asingle bare elongate member of substantially U-shaped transversecross-section, the space between the limbs and base of the U-shapeextending throughout the length of the core and constituting (the) anelongate compartment; at least one separate flexible optical guideloosely housed in the elongate compartment; and, surrounding the centralcore, at least one stranded layer of helically wound bare elongateelements of metal or metal alloy.
 5. An overhead flexible electrictransmission conductor as claimed in claim 4, wherein at least one ofthe limbs of the U is folded inwardly so that the gap between the freeends of the limbs is at least partially closed.
 6. An overhead flexibleelectric transmission conductor as claimed in claim 4 wherein the gapbetween the free ends of the limbs of the U is closed by at least onetape of metal or metal alloy which is applied around the U-shapedelongate member.
 7. An overhead flexible electric transmission conductor(as claimed in claim 15, wherein) adapted to be freely supported fromspaced supports in long lengths comprising at least one stranded layerof helically wound bare elongate elements of metal or metal alloy, saidbare elongate elements (have) having a transverse cross-sectional shapeapproximating to a sector of an annulus and at least one of the abuttingfaces of (said) adjacent elongate elements having an elongate recesswhich is closed by the flat surface of the other of the abutting facesto form an elongate space which constitutes an elongate compartmentextending throughout the length of the layer and, loosely housed in theelongate compartment or at least one of the elongate compartments, atleast one separate flexible optical guide.
 8. An overhead flexibleelectric transmission conductor as claimed in claim 4, wherein the oreach separate flexible optical guide in the elongate compartment or inat least one of the elongate compartments is supported by a flexibleelongate carrier member which is loosely housed in the elongatecompartment.
 9. An overhead flexible electric transmission conductor asclaimed in claim 1 or 4, wherein the flexible optical guide or at leastone of the flexible optical guides is a separate optical fiber.
 10. Anoverhead flexible electric transmission conductor as claimed in claim 1or 4, wherein the flexible optical guide or at least one of the flexibleoptical guides is an optical bundle.
 11. An overhead flexible electrictransmission conductor as claimed in claim 1 or 4, wherein the or eachseparate flexible optical guide and the elongate compartment in which itis loosely housed are of approximately equal lengths.
 12. An overheadflexible electric transmission conductor as claimed in claim 4, whereinthe limbs of the U are folded together so that the gap between the freeends of the limbs is closed.
 13. An overhead flexible electricaltransmission conductor as claimed in claim 4 wherein the limbs of theU-shaped elongate member are closed to form a circular section.